1. Field of the Invention
This invention relates to a dual belt conveyor for continuous paper tubing which may have adhesive-bonded longitudinal seams in the middle portions of the upper plies, and which conveyor preferably precedes a tear-off dual belt conveyor moving at a higher speed serving to retain the last but one length section of the paper tubing, when a transverse perforation line at which the tubing is to be severed is disposed between the two dual belt conveyors, and wherein reversing pulleys and backing rollers for the conveyor belt or belts on the underside of the path of the continuous paper tubing are longitudinally offset from reversing pulleys and backing rollers on the upper side of said path, so that the paper tubing is moved through the dual belt conveyor along an undulating path.
2. Description of the Prior Art
In a dual belt conveyor as disclosed, for example, in European Patent No. 0 96 223, a wave may form in the top ply of the continuous paper tubing before the entry gap of the dual belt conveyor. The wave can be subsequently pulled into the nip of the conveyor and compressed by the belts so that sacks made from the paper tubing have a poor appearance and considerable difficulties can arise in further processing.
The formation of a wave before the entry gap of the dual belt conveyor is due to the fact that flat continuous paper tubing unwound from a roll may be somewhat longer at its edge portions than its intermediate portion. The difference in length may be about 1 mm per 1000 mm length of the continuous paper tubing.